Bubble domains arranged in a lattice are described in U.S. Pat. Nos. 3,930,244 and 4,052,710 which are assigned to the assignee of the present invention. The aforementioned patents are incorporated herewith by reference thereto. As described therein the bubble domain lattice consists of a plurality of rows and columns of bubble domains which occupy a spatial arrangement which is determined to a substantial extent by the interaction between the bubbles.
Heretofore bubble domain lattices have been in the form of a parallelogram in which there are parallel rows and columns of bubble domains. In current bubble domain lattice system designs the bubbles are translated parallel to the rows of the storage axis to position the addressed bubbles in an access channel. When the bubbles are in the access channel, these bubbles can be translated within the lattice along the channel. Such translation along the column axis is used to enter new bubbles into the lattice and to remove existing bubbles from the lattice.
Present designs of bubble lattice systems all rely on rectilinear lattice translation for data accessing. This requires means for bidirectional lattice translation and buffer regions on both sides of the lattice. In certain applications in which buffer regions of this type are not suitable, the bubble lattice requires some type of closed loop arrangement.
A bubble lattice system having a closed loop design has certain problems. A primary problem or obstacle would be that the lattice boundary cannot follow a straight line as with the standard lattice designs because the closed loop bubble lattice systems require at least one curved lattice segment. Maintaining a regular lattice in a curved portion presents a problem which must be overcome in order to have a satisfactory closed loop lattice system. In any curved portion a regular lattice is retained only if the lattice parameter increases with the radius of curvature. Unless the outer lattice boundary is very close to the inner lattice boundary, a regular lattice arrangement is not maintained throughout the whole curved segment.
One approach to a closed loop lattice system is described in U.S. Pat. No. 3,953,841, assigned to the assignee of the present invention, in which the bubble lattice system has a curved portion therein wherein the lattice parameter increases with the radius. Associated with the curved portion in a preferred embodiment is a radially varying bias field wherein the strength of said field at any position occupied by a bubble domain provides an equilibrium lattice constant which is substantially the same as the lattice parameter at that position. The method of reducing the stress in the curved portion of a bubble domain lattice system involves the step of varying the parameters which affect the equilibrium lattice constant in such a manner as to provide an equilibrium lattice constant which is substantially the same as the lattice parameter at any given position in the curved portion.